1. Field of the Invention
The present invention relates generally to a prosthetic foot. More particularly, the present invention relates to a prosthetic foot with a composite heel operable to simulate the flexion normally provided by an anatomical ankle.
2. Background of the Invention
A useful prosthesis must simulate the operation and motion of an anatomical foot. In addition, for Syme amputees (e.g., amputees who have sustained an ankle disarticulation), a useful prosthesis must simulate the operation, flexion, and motion of an anatomical ankle.
An anatomical foot, including the ankle joint, is capable of motion around three perpendicular axes, as well as varying degrees of flexure. Specifically, the anatomical foot and ankle are capable of dorsiflexion, planiflexion, inversion, eversion, and transverse rotation. Dorsiflexion and planiflexion comprise the movement of the ball of the foot upward and downward, respectively, with respect to the heel. Inversion and eversion are the twisting of the foot around its longitudinal axis, resulting in outward and inward tilting of the ankles, respectively. Transverse rotation occurs when the foot rotates with respect to the longitudinal axis of the leg, such as occurs during left and right turns of the body.
Some prosthetic feet that include an ankle prosthesis may be capable of complicated motion (e.g., motion around two or three axes). In particular, such prostheses may be useful for Syme amputees since the inclusion of a prosthetic ankle may simulate the operation, flexion, and motion normally provided by an anatomical ankle. However, inclusion of a prosthetic ankle may add bulky moving parts and additional weight to the prosthesis. The additional weight may result in a prosthesis that is too heavy for some patients, such as geriatric patients, very young patients, or other patients who suffer some degree of muscular weakness.
Moreover, although some flexibility may be desirable, a prosthetic foot must also provide a secure and relatively rigid means for coupling the prosthetic foot to the amputee. Some conventional prosthetic feet may provide a rigid metal plate that is bolted to the prosthetic foot to couple the prosthetic foot to the amputee. However, the use of a metal plate may add additional bulk and reduce the flexibility of the prosthetic foot, as well as create stress concentration areas in the prosthetic foot around the bolt attachment points. Concentration of stresses proximal to the areas where the prosthetic foot flexes may lead to premature weakening, cracking, or breaking of the prosthetic foot.
In addition, it is desirable for a prosthetic foot to provide a spring effect during use (e.g., be capable of absorbing, storing, and releasing energy). At a minimum, the prosthesis should store enough energy to return itself to a relaxed, unflexed position when external forces are removed. Such a spring effect may be accomplished by the inclusion of energy storing components such as coil springs. However, such energy-storing components may significantly increase the weight of the prosthesis.
Finally, it is necessary that a prosthetic foot be strong enough to support its wearer and durable enough to withstand the stresses of repeated stepping motions over long periods of time. Some conventional prostheses may be designed for maximize strength, at the cost of added bulk and weight, making them unsuitable for some amputees.
Thus, there remains a need to develop methods and apparatus for improved foot prostheses which overcome some of the foregoing difficulties while providing more advantageous overall results.